Method for supplying solder

ABSTRACT

Obtained are fine-pitched pad electrodes and also solder bumps with a large amount of solder and a less difference in the amount. First, in an inert liquid ( 13 ) in a liquid tank ( 11 ), a substrate ( 20 ) is positioned with a surface ( 21 ) facing up. Subsequently, the inert liquid ( 13 ) containing solder fine particles ( 14 ) is fed from a solder fine particle forming unit ( 15 ) to the liquid tank ( 11 ) and the solder fine particles ( 14 ) are dropped from a supply pipe ( 16 ) onto the substrate ( 20 ) in the inert liquid ( 13 ). The solder fine particles ( 14 ) naturally fall down by the gravity, thereby reaching the substrate ( 20 ). The solder fine particles ( 14 ) reached on the pad electrodes on the substrate ( 20 ) stay there due to the gravity, and spread on the surfaces of the pad electrodes after the solder wet time, thereby forming solder coating.

TECHNICAL FIELD

The present invention relates to a solder supplying method which is, forexample, used when manufacturing FC (flip chip) and BGA (ball gridarray) by forming hemispherical solder bumps on a semiconductorsubstrate and on an interposer substrate, and to a method and anapparatus for forming solder bumps using the same.

BACKGROUND ART

In recent years, a high density mounting technology of electroniccomponents has been making a rapid progress in accordance withminiaturization and thinning of electronic devices. FC and BGA with thehemispherical solder bumps are used as semiconductor devices forachieving the high density mounting.

As a method for forming solder bumps on pad electrodes, generally usedare a method in which pad electrodes are made to be in contact withmolten solder (molten solder method), a method in which solder paste isscreen-printed on pad electrodes and is re-flown (screen printingmethod), a method in which solder balls are mounted on pad electrodesand are re-flown (solder ball method), a method in which solder platingis applied on pad electrodes (plating method), etc. In addition, thereis another known method for forming solder bumps as disclosed inJapanese Patent Unexamined Publication No. 7-114205 (FIG. 1, etc), forexample.

FIG. 4 is a schematic cross section for showing the forming methoddisclosed in Japanese Patent Unexamined Publication No. 7-114205. Itwill be described in the followings by referring to the drawing.

In this forming method, first, in an inert solvent 80 which is heated tobe hotter than a melting point of solder, a wafer 82 having copperelectrodes 81 on a surface is immersed with the surface facing down.Then, in the inert solvent 80, solder particles 84 made of molten solder83 are emitted upwards. Thereby, solvent bumps (not shown) are formed onthe copper electrode 81 by making the solder particles 84 come incontact with the wafer 82. It will be described in more detail.

The molten solder 83 and the inert solvent 80 inside a heat tank 85 arecontrolled to be at temperatures slightly higher than a melting point ofsolder, for example, at 200° C. The molten solder 83 inside the heattank 85 is sucked into a solder-fine-particle forming unit 87 through asolder intake pipe 86. Further, the solder-fine-particle forming unit 87sucks the inert solvent 80 which is at the same temperature as that ofthe molten solder 83 through an inert solvent intake pipe 88 andmixes/agitates these two liquids for breaking the molten solder 83 so asto have it pulverized. Then, the inert solvent 80 containing the solderparticles 84 is transferred to an ejection unit 90 through amixed-solution outlet pipe 89 to be emitted upwards from nozzles 91.

The solder particles 84 in the inert solvent 80 are coated by the inertsolvent 80 so that they are not to be exposed to the open air. Thus, thesurfaces of the solder particles 84 maintain the metal surfaces to be inan active state. The solder particles 84 in the inert solvent 80, whenin contact with the surface of the immersed wafer 82, form a solderalloy layer together with the copper electrodes 81 and stick to thesurfaces thereof. Thereby, the surfaces of the copper electrodes 81 arecovered by the molten solder coating (not shown). Subsequently, sincethe solder particles 84 are easily adsorbed to the solder coating sothat the solder particles 84 in this part are stuck onto the soldercoating one after another.

In the meantime, the solder particles 84 which do not stuck onto thecopper electrodes 81 gradually fall down due to the specific gravitydifference and deposit in the bottom of the heat tank 85. As describedabove, by immersing the wafer 82 with the copper electrodes 81 facingdown in the inert solvent 80 where the solder particles 84 are emittedupwards, the solder bumps (not shown) can be selectively formed on thesurfaces of the copper electrodes 81.

However, in the molten solder method, there is such a drawback thatthere is a small amount of the solder in the solder bumps and thedifference in the amount is large, while it is suitable for achievingfine pitch of the pad electrodes. In the silk screen printing method, itis not suitable for achieving the fine pitch since it is likely to causeclogging and uneven solder amount when using a mask with the fine pitch,while it enables to easily form the solder bumps collectively. In thesolder ball method, as the recent trend, the number of solder balls usedin a single semiconductor device is extremely large and, in addition,the size of the solder balls are extremely small so that it increasesthe manufacturing cost. In the plating method, there is no platingliquid appropriate for lead-free solder which has recently come intouse. In the forming method as disclosed in Japanese Patent UnexaminedPublication No. 7-114205, there is such a drawback that the solderparticles are not easily stuck to the copper electrode, i.e. the solderwetability is not great, so that it is difficult to put it intopractical use.

Therefore, the object of the present invention is to provide a soldersupplying method, which enables to achieve fine-pitched pad electrodesand also to obtain solder bumps with a large amount of solder and asmall difference in the amount thereof, and to provide a method and anapparatus for forming the solder bumps using the same.

DISCLOSURE OF THE INVENTION

The solder supplying method according to claim 1 is a method in whichsolder coating is formed on a metal film through positioning a substratehaving the metal film on a surface with the surface facing up in aliquid which is heated to be hotter than a melting point of solder anddropping solder fine particles made of the melted solder on thesubstrate in the liquid. The “solder” herein is not limited only to thesolder for forming solder bumps but also includes solder for die-bondingsemiconductor chips and “soft solder” and the like used for, forexample, bonding copper pipes. Naturally, it also includes lead-freesolder. It is preferable that the “liquid” used herein be an inertliquid which does not react to the solder and a liquid (for example, anorganic acid and the like to be described later) which has an effect ofremoving an oxide film on the surface of the solder. The “soldercoating” herein is not limited only to a film type but also includes ahemispherical type and a protrusion type.

In the liquid, the substrate is immersed with the metal film side facingup. At this time, when the solder fine particles are supplied into theliquid above the substrate, the solder fine particles naturally falldown due to the gravity, thereby reaching on the substrate. The solderfine particles fallen onto the metal film of the substrate stay there bythe gravity and then spread on the metal film surface after “a certaintime”, so as to form the solder coating. Subsequently, the solder fineparticles reached on the solder coating stay there by the gravity andspread as well after “a certain time, thereby thickening the soldercoating. This action is repeated and the solder coating is grown.

The Inventor of the present invention has found out that it requires “acertain time” (referred to as “solder wet time” hereinafter) asdescribed above for the solder to be wet. In the art disclosed inJapanese Patent Unexamined Publication No. 7-114205, the solder fineparticles are emitted towards the pad electrodes facing downwards formaking them come in contact, so that the time for the solder fineparticles to be in contact with the pad electrodes is only a moment.Therefore, it is considered that the solder wetability is not good.

Further, in the art of Japanese Patent Unexamined Publication No.7-114205, the solder fine particles are emitted against the gravity sothat it requires a considerable amount of energy. On the contrary, inthe present invention, the solder fine particles are only left tonaturally fall down so that it requires almost no energy. The art ofJapanese Patent Unexamined Publication No. 7-114205 can be considered asa kind of jet soldering. Meanwhile, the present invention is completelya new technique which does not belong to any of the conventionalsoldering methods.

The Inventor of the present invention also found out that there are notmany solder fine particles which are combined for forming larger solderfine particles, even if the solder fine particles come in contact witheach other in the liquid. Therefore, the solder bridges and the like arenot generated even in the metal films with the fine pitch. Further, thesolder amount of the solder coating can be easily controlled by changingthe supply amount of the solder fine particles. Moreover, since thesolder fine particles are extremely small, a large amount can besupplied so that they can be uniformly dispersed in the liquid.Therefore, the difference in the solder amount in the solder coatingbecomes small.

The solder supplying method according to claim 2 is the method in whichthe solder fine particles, which are dropped and come in contact withthe metal film or the solder coating, are kept for a certain time inthat state until solder wet is caused in the solder supplying methodaccording to claim 1. “A certain time until the solder wet is caused” isthe solder wet time described above. Thus, it is possible to surelycause the solder wet by keeping the solder fine particles in contactwith the metal film or the solder coating in that state for the solderwet time or longer. The “solder wet” herein is not limited to formingthe solder coating formed on the metal film surface by spread of thesolder fine particles reached on the metal film but also includesthickening of the solder coating by spread of the solder fine particlesreached on the solder coating.

The solder supplying method according to claim 3 is the method in whichthe solder fine particles to be dropped on the substrate is limited tothe ones whose falling speed is within a specific range in the soldersupplying method according to clam 1 or 2. As for the solder fineparticles in the liquid, the larger ones are faster in the falling speedand the smaller ones are slower in the falling speed. Meanwhile, whenthe size of the solder fine particles is large, it is likely to generatethe solder bridge. When the size of the solder fine particles is small,the surface is easily oxidized. Therefore, by selecting the solder fineparticles with the falling speed within a specific range, it enables tosuppress the generation of the solder bridges and deterioration of thesolder wetability by the oxide film. Specifically, it can be achieved bydropping a large amount of the solder fine particles all at once, and byretreating the substrate or covering the substrate with a shutter at thetime when the larger solder fine particles fall in the vicinity of thesubstrate and when the smaller solder fine particles fall in thevicinity of the substrate so that the solder fine particles do not reachthe substrate.

The solder bump forming method according to claim 4 is the method forforming a solder bump on a pad electrode through: positioning asubstrate having the pad electrode on a surface with the surface facingup in a liquid which is heated to be hotter than a melting point ofsolder; supplying solder fine particles made of the solder being meltedinto the liquid; and dropping the solder fine particles on thesubstrate. The “substrate” herein includes a semiconductor wafer, awiring board, and the like. Further, the “solder bump” is not limited tothe ones of a hemispherical type or a protrusion type but also include afilm type.

In the liquid, the substrate is immersed with the pad electrode sidefacing up. At this time, when the solder fine particles are suppliedinto the liquid over the substrate, the solder fine particles naturallyfall down due to the gravity, thereby reaching the substrate. The solderfine particles fallen onto the pad electrode of the substrate stay thereby the gravity and then spread on the surface of the pad electrode afterthe solder wet time, so as to form the solder coating. Subsequently, thesolder fine particles reached on the solder coating stay there by thegravity and spread as well after the solder wet time, thereby thickeningthe solder coating. This action is repeated and the solder coating isgrown to be the solder bump.

As described above, the Inventor of the present invention has found outthat there are not many solder fine particles which are combined forforming larger solder fine particles, even when the solder fineparticles come in contact with each other in the liquid. Therefore, thesolder bridges and the like are not generated even in the pad electrodeswith the fine pitch. Further, the solder amount of the solder bump canbe easily controlled by changing the supply amount of the solder fineparticles. Moreover, since the solder fine particles are extremelysmaller than the pad electrode, a large amount can be supplied so thatthey can be uniformly dispersed in the liquid. Therefore, the differencein the solder amount in the solder bumps becomes small.

The solder bump forming method according to claim 5 is the method inwhich the solder fine particles are formed by breaking the solder beingmelted in the liquid in the forming method according to claim 4. Thesolder fine particles and the solder bumps are formed in a common liquidso that the forming apparatus can be simplified.

The solder bump forming method according to claim 6 or 7 is the methodin which flux or an organic acid is contained in the liquid or theliquid is made of the organic acid, and the organic acid has a reductioneffect which removes an oxide on a metal surface in the forming methodaccording to claim 4 or 5. By the effect of the flux or the organicacid, the solder wetability in the liquid is more improved. The “flux”herein includes colophony, a surface active agent, a substance (forexample, hydrochloric acid) having an effect of removing the oxide filmon the solder surface and the like.

The solder bump forming method according to claim 8 is the method inwhich a diameter of the solder fine particle is smaller than a shortestdistance between peripheral edges of the pad electrodes adjacent to eachother in the forming method according to any one of claims 4 to 7. Inthis case, the solder fine particles reached respectively on the twoadjacent pad electrodes are not to be in contact with each other, sothat they are not to be combined for forming the solder bridge.

The solder bump forming apparatus according to claim 9 comprises aliquid tank and a solder fine particle supplying means. The liquid tankencloses a liquid heated to be hotter than a melting point of solder anda substrate which has pad electrodes on a surface and is positioned inthe liquid with the surface facing up. The solder fine particlesupplying means supplies the solder fine particles made of the solderbeing melted into the liquid and drops the solder fine particles on thesubstrate.

In the liquid inside the liquid tank, the substrate is immersed with thepad electrode side facing up. At this time, when the solder fineparticles are supplied from the solder fine particle supplying meansinto the liquid above the substrate, the solder fine particles naturallyfall down by the gravity, thereby reaching on the substrate. The sameeffects as those in the forming method according to claim 4 can beachieved hereinafter.

The solder bump forming apparatus according to claim 10 is the apparatusin which the solder fine particle supplying means forms the solder fineparticles through breaking the solder being melted in the liquid in theforming apparatus according to claim 9. The same effect as those in theforming method according to claim 5 can be achieved.

The solder bump forming apparatus according to claim 11 is the apparatusin which the liquid tank and the solder fine particles supplying meanshave the following configurations in the forming apparatus according toclaim 10. The liquid tank comprises a first liquid tank for enclosingthe substrate and the liquid and a second liquid tank for enclosing theliquid and the solder being melted and sunk in the liquid. Uppersections of the first liquid tank and the second liquid tank communicatewith each other while bottom sections do not. The solder fine particlesupplying means forms the solder fine particles through breaking thesolder being melted in the second liquid tank and supplies the solderfine particles to the first liquid tank from the upper section of thesecond liquid tank.

In the liquid inside the first liquid tank, the substrate is immersedwith the pad electrode side facing up. At this time, the solder fineparticle supplying means supplies the solder fine particles into theliquid above the substrate inside the first liquid tank from the uppersection of the second liquid tank. Upon this, the solder fine particlesnaturally fall down due to the gravity, thereby reaching on thesubstrate. The solder fine particles fallen onto the pad electrodes ofthe substrate stay there by the gravity and then spread on the surfacesof the pad electrodes after the solder wet time, thereby forming thesolder coating. Then, the solder fine particles fallen onto the soldercoating stay there by the gravity and then spread as well after thesolder wet time, thereby thickening the solder coating. This action isrepeated and the solder coating is grown to be the solder bumps.

In the meantime, the solder fine particles which did not form the solderbumps sink in the bottom of the first liquid tank. However, since thebottom sections of the first liquid tank and the second liquid tank donot communicate with each other, the deposited solder fine particles arenot to be broken so as to become the solder fine particles again.Therefore, the quality of the solder fine particles as the base for thesolder bumps becomes stable and the size can be made uniform.

The solder bump forming apparatus according to claim 12 is the formingapparatus in which the liquid tank and the solder fine particlesupplying means have the following configurations in the formingapparatus according to claim 10. The liquid tank comprises: a firstliquid tank for enclosing the substrate, the liquid and the solder beingmelted and sunk in the liquid; and a second liquid tank for enclosingthe liquid and the solder being melted and sunk in the liquid. The uppersections and bottom sections of the first liquid tank and the secondliquid tank communicate with each other. The solder fine particlesupplying means forms the solder fine particles through breaking themolten solder in the first liquid tank and the second liquid tank,supplies the solder fine particles to the first liquid tank from theupper section of the second liquid tank, and reutilizes the solder fineparticles sunk in a bottom of the first liquid tank as the moltensolder.

The process for forming the solder bumps by the solder fine particles isthe same as the forming apparatus according to claim 11. Meanwhile, thesolder fine particles which did not form the solder bumps sink in thebottom of the first liquid tank. Then, since the bottom sections of thefirst liquid tank and the second liquid tank communicate with each otherso that the deposited solder fine particles are broken and utilizedagain as the solder fine particles. Therefore, solder can be effectivelyutilized.

The solder bump forming apparatus according to claim 13 or 14 is theapparatus in which flux or an organic acid is contained in the liquid orthe liquid is made of the organic acid, and the organic acid has areduction effect which removes an oxide on a metal surface in theforming apparatus according to any one of claims 9 to 12. The sameeffect as those in claim 6 or 7 can be achieved.

The solder bump forming apparatus according to claim 15 is the apparatusin which a diameter of the solder fine particle is smaller than ashortest distance between peripheral edges of the pad electrodesadjacent to each other in the forming apparatus according to any one ofclaims 9 to 14. The same effects as those in claim 8 can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 are schematic block diagrams showing a first embodiment of amethod and an apparatus used for forming solder bumps, in which thesteps are carried out in order from FIG. 1[1] to FIG. 1[3];

FIGS. 2 are fragmentary enlarged views of FIGS. 1, in which FIG. 2[1] toFIG. 2[3] correspond to FIG. 1[1] to FIG. 1[3], respectively;

FIG. 3 is a schematic block diagram showing a second embodiment of amethod and an apparatus used for forming solder bumps; and

FIG. 4 is a schematic block diagram showing a conventional solder bumpforming method.

BEST MODE FOR CARRYING OUT THE INVENTION

In the followings, embodiments of the present invention will bedescribed by referring to the accompanying drawings. The soldersupplying method according to the present invention is used in themethod and the apparatus for forming the solder bumps according to thepresent invention, so that it will be described together in thedescription provided for explaining the method and the apparatus forforming the solder bumps of the present invention.

FIGS. 1 are schematic block diagrams showing a first embodiment of themethod and the apparatus used for forming solder bumps, in which thesteps are carried out in order from FIG. 1[1] to FIG. 1[3]. Descriptionwill be provided in the followings by referring to the drawings.

A forming apparatus 10 used in the embodiment will be described. Theforming apparatus 10 comprises a liquid tank 11 and a solder fineparticle supplying means 12. The liquid tank 11 encloses an inert liquid13 as a liquid which is heated to be hotter than the melting point ofsolder and a substrate 20 which is positioned in the inert liquid 13with a surface 21 facing up. The solder fine particle supplying means 12comprises a solder fine particle forming unit 15 for supplying solderfine particles 14 made of molten solder into the inert liquid 13 and asupply pipe 16 for dropping the solder fine particles 14 on thesubstrate 20.

Examples of the solder to be used are Sn—Pb (melting point at 183° C.),Sn—Ag—Cu (melting point at 218° C.), Sn—Ag (melting point at 221° C.),Sn—Cu (melting point at 227° C.), etc. The inert liquid 13 may be anytypes of liquid as long as it has a boiling point higher than themelting point of the solder and that it does not react to the solder(for example, fluorinated high boiling point solvent, fluorinated oiland the like). The liquid tank 11 is obtained by placing an electricheater and a coolant and the like (not shown) for keeping the inertliquid 13 higher than the melting point of the solder (for example,melting point +50° C.) in a container made of, for example, stainless,heat-resistant resin and the like. Further, inside the liquid tank 11, amount 17 is provided for positioning the substrate 20 in the inertliquid 13.

The solder fine particle forming unit 15 is for forming the solder fineparticles 14 by, for example, breaking the molten solder in the inertliquid 13. In this case, a laying pipe, which is for taking-in thesolder fine particles 14 (molten solder) sunk in the bottom of theliquid tank 11 and the inert liquid 13 inside the liquid tank 11, may beprovided in between the liquid tank 11. In the supply pipe 16, forexample, a large number of supply ports (not shown) are provided from anedge to the other edge, and the solder fine particles 14 are droppeduniformly from the supply ports into the inert liquid 13. Thereby, thesolder fine particles 14 mixed in the inert liquid 13 are fed outthrough the solder fine particle forming unit 15 and dropped into theinert liquid 13 inside the liquid tank 11 from the supply pipe 16.

FIGS. 2 are fragmentary enlarged views of FIGS. 1, in which FIG. 2[1] toFIG. 2[3] correspond to FIG. 1[1] to FIG. 1[3], respectively.Description will be provided in the followings by referring to thedrawings. Description of the same components as those of FIGS. 1 will beomitted by applying the same reference numerals thereto. FIGS. 2 aremore enlarged in vertical direction than in the lateral direction.

First, the substrate 20 used in the embodiment will be described. Thesubstrate 20 is a silicon wafer. On the surface 21 of the substrate 20,pad electrodes 22 are formed. On the pad electrodes 22, solder bumps 23are formed by the forming method of the embodiment. The substrate 20 iselectrically and mechanically connected to other semiconductor chips andwiring boards through the solder bumps 23. The shape of the padelectrode 22, for example, is a circular shape and has a diameter c of,for example, 40 μm. A distance d between the centers of the adjacent padelectrodes 22 is 80 μm, for example. A diameter b of the solder fineparticles 14 is, for example, 3 to 15 μm.

The pad electrode 22 is made of an aluminum electrode 24 formed on thesubstrate 20, a nickel layer 25 formed on the aluminum electrode 24, anda gold metal layer 26 formed on the nickel layer 25. The nickel layer 25and the gold metal layer 26 are UBM (under barrier metal or under bumpmetallurgy) layers. The part of the substrate 20 other than the area ofthe pad electrodes 22 is covered by a protective film 27.

Next, the forming method of the pad electrodes 22 will be described.First, the aluminum electrode 24 is formed on the substrate 20 and theprotective film 27 is formed by polyimide resin in the part where thealuminum electrode 24 is not formed. These are formed, for example, byphotolithography and etching. Then, after applying a zincate treatmenton the surface of the aluminum electrode 24, the nickel layer 25 and thegold metal layer 26 are formed on the aluminum electrode 24 by usingelectroless plating. The UBM layer is provided for giving the solderwetability to the aluminum electrode 24.

Next, the function and effect of the method and the apparatus forforming the solder bumps according to the embodiment will be describedby referring to FIG. 1 and FIGS. 2.

First, as show in FIG. 1[1] and FIG. 2[1], in the inert liquid 13 in theliquid tank 11, the substrate 20 is positioned with the surface 21facing up. The pad electrodes 22 are formed on the surface 21 of thesubstrate 20. The inert liquid 13 is heated to be hotter than themelting point of the solder.

Subsequently, as shown in FIG. 1[2] and FIG. 2[2], the inert liquid 13containing the solder fine particles 14 is fed from the solder fineparticle forming unit 15 to the liquid tank 11 and the solder fineparticles 14 are dropped from the supply pipe 16 onto the substrate 20in the inert liquid 13.

In the inert liquid 13, the substrate 20 is immersed with the electrodepad 22 side facing up. At this time, when the solder fine particles 14are supplied into the inert liquid 13 above the substrate 20, the solderfine particles 14 naturally fall down by the gravity, thereby reachingthe substrate 20. The solder fine particles 14 reached on the padelectrodes 22 on the substrate 20 stay there due to the gravity, andspread on the surface of the pad electrodes 22 after the solder wet timefor forming solder coating 23′. Then, the solder fine particles 14reached on the solder coating 23′ stays there due to the gravity, andalso spread for thickening the solder coating 23′ after the solder wettime as well. These actions are repeated and the solder coating 23′ isgrown to be the solder bump 23 (FIG. 1[3] and FIG. 2[3]).

The solder wet time is the time by which the solder fine particles 14and the pad electrodes 22 or the solder coating 23′ come to be incontact, i.e. the time necessary for the solder to be wet (for exampleseveral seconds to some ten seconds), which is found by the Inventor ofthe present invention. In the embodiment, when the solder fine particles14 fall down and reach the pad electrodes 22 or the solder coating 23′,the solder fine particles 14 stay there due to the effect of thegravity. Thus, the solder fine particles 14 and the pad electrodes 22 orthe solder coating 23′ are to be in contact until the solder wet timehas passed. Therefore, the solder wetability is excellent.

Further, the Inventor has found out that there are not many solder fineparticles 14 which are combined for forming larger solder fine particleseven if when the solder fine particles 14 come in contact with eachother in the inert liquid 13. Therefore, solder bridges and the like arenot generated even in the pad electrodes 22 formed with a fine pitch.Especially, it is better to make the diameter b of the solder fineparticle 14 smaller than a shortest distance a between peripheral edgesof the adjacent pad electrodes 22. In this case, the solder fineparticles 14 which respectively reached on the two adjacent padelectrodes 22 do not come in contact, so that they are not combined forforming the solder bridge.

Further, the solder amount in the solder bump 23 can be easilycontrolled through changing the supply amount of the solder fineparticles 14 by the solder fine particle forming unit 15. Moreover,since the solder fine particle 14 is extremely smaller than the padelectrode 22, a large amount of the solder fine particles 14 aresupplied so as to be uniformly dispersed in the inert liquid 13.Therefore, there is a less difference in the solder amount of the solderbumps 23.

FIG. 3 is a schematic block diagram for showing a second embodiment ofthe method and the apparatus for forming the solder bumps according tothe present invention. Description will be provided in the followings byreferring to the drawing. Description of the same components as those ofFIGS. 1 and FIGS. 2 will be omitted by applying the same referencenumerals thereto.

In a solder bump forming apparatus 30 of the embodiment, a liquid tank31 and a solder fine particle supplying means 32 are in theconfigurations as follows. The liquid tank 31 comprises: a liquid tank34 for enclosing a substrate 20, an inert liquid 13, and molten solder33 sunk in the inert liquid 13; and liquid tanks 35, 36 for enclosingthe inert liquid 13, and the molten solder 33 sunk in the inert liquid13. The liquid tank 34 and the liquid tanks 35, 36 communicate with eachother through upper sections 37 and bottom sections 38.

The solder fine particle supplying means 32 comprises agitators 32A, 32Bplaced in the liquid tanks 35, 36. It forms the solder fine particles 14by breaking the molten solder 33 inside the liquid tanks 34 to 36, whilesupplying the solder fine particles 14 into the liquid tank 34 from theupper sections 37 of the liquid tanks 35, 36 for reutilizing the solderfine particles 14 sunk in the bottom section 38 of the liquid tank 34 asthe molten solder 33.

Next, the action of the forming apparatus 30 will be described. Theagitators 32A, 32B have the same configuration so that only the agitator32A will be described.

The agitator 32A is placed in the liquid tank 35 and comprises a motor40, a rotating shaft 41, an impeller 42, and the like. When the motor 40rotates, the impeller 42 is also rotated through the rotating shaft 41.Upon this, the impeller 42 generates a flow of the inert liquid 13 whichcirculates inside the liquid tanks 34, 35. Then, the molten solder 33inside the liquid tank 35 is caught in the flow and broken by theimpeller 42 to be the solder fine particles 14 for being supplied intothe liquid tank 34 from the upper section 37.

The process of forming the solder bumps (not shown) by the solder fineparticles 14 is the same as that of the first embodiment. In themeantime, the solder fine particles 14 which did not form the solderbumps sink in the bottom section 38 inside the liquid tank 34. Theliquid tank 34 and the liquid tank 35 communicate with each otherthrough the bottom sections 38, so that the deposited solder fineparticles 14 are broken to be the molten solder 33 and utilized again asthe solder fine particles 14. Therefore, the solder can be effectivelyutilized.

The space between the liquid tank 34 and the liquid tank 35 may be shutso that they do not communicate with each other through the bottomsections 38. In this case, the solder fine particles 14 are notreutilized. Therefore, the quality of the solder fine particles 14 isimproved and the size of the solder fine particles 14 becomes moreuniform.

Needless to say, the present invention is not limited the first and thesecond embodiments described above. For example, instead of a siliconwafer (FC), a wiring board (BGA) may be used. Further, flux or theabove-described organic acid may be contained in the inert liquid, orthe above-described organic acid may be used instead of the inertliquid. Moreover, the electrode material is not limited to aluminum butAl—Si, Al—Si—Cu, Al—Cu, Cu, or the like may be used. Furthermore, afterremoving the oxide film of the solder fine particles by, for example,hydrochloric acid, the solder fine particles may be introduced into theliquid.

INDUSTRIAL APPLICABILITY

With the solder supplying method (claim 1) according to the presentinvention, by forming a solder coating on a metal film by droppingsolder fine particles on a substrate in a liquid which is heated to behotter than the melting point of solder, the solder fine particlesreached on the metal film can be kept there due to the gravity for thetime longer than the solder wet time. Thereby, the solder wetability canbe improved. Further, there are not many solder fine particles which arecombined to be larger solder particles even if the solder fine particlescome in contact with each other in the liquid, so that it enables toprevent solder bridges and the like from being formed in the metal filmswith a fine pitch. Furthermore, by changing the supply amount of thesolder fine particles, the solder amount in the solder coating can beeasily controlled. Moreover, since the solder fine particle is extremelysmall, a large amount of the solder fine particles are supplied so as tobe uniformly dispersed in the liquid. Therefore, the solder amount inthe solder coating can be made uniform. As a result, it enables toobtain the metal films with the fine pitch and also enables to obtainthe solder coating with a large amount of solder and a less differencein the amount.

With the solder supplying method according to claim 2, by keeping thesolder fine particles which are in contact on the metal film or thesolder coating in that state for longer than the solder wet time, it ispossible to surely cause the solder wet.

With the solder supplying method according to claim 3, by dropping on asubstrate the solder fine particles which have the falling speed withina specific range, only the solder fine particles in an appropriate sizecan be used. Therefore, it is possible to suppress generation of thesolder bridges and deterioration of the solder wetability due to theoxide film.

With the method and the apparatus for forming the solder bumps accordingto the present invention (claims 4, 9), by forming the solder bumps onthe pad electrodes through dropping the solder fine particles on thesubstrate in the liquid which is heated to be hotter than the meltingpoint of the solder, the solder fine particles reached on the padelectrodes can be kept there due to the gravity for the time longer thanthe solder wet time. Thereby, the solder wetability can be improved.Further, there are not many solder fine particles which are combined tobe larger solder fine particles even if the solder fine particles comein contact with each other in the liquid, so that it enables to preventsolder bridges and the like from being formed in the pad electrodes witha fine pitch. Furthermore, by changing the supply amount of the solderfine particles, the solder amount in the solder bumps can be easilycontrolled. Moreover, since the solder fine particle is extremelysmaller than the pad electrodes, a large amount of the solder fineparticles are supplied so as to be uniformly dispersed in the liquid.Therefore, the solder amount in the solder bumps can be made uniform. Asa result, it enables to obtain the pad electrodes with a fine pitch andalso enables to obtain the solder bumps with a large amount of solderand a less difference in the amount.

With the method and the apparatus for forming the solder bumps accordingto the present invention (claims 5, 10), by forming the solder fineparticles through breaking the molten solder in the liquid, the solderfine particles and the solder bumps can be formed in a common liquid.Thereby, the configuration of the forming apparatus can be simplified.

In the method and the apparatus for forming the solder bumps accordingto the present invention (claims 6, 7, 13, 14), flux or theabove-described organic acid is contained in the liquid, or the liquidis made of the organic acid, so that the solder wetability in the liquidcan be more improved.

With the method and the apparatus for forming the solder bumps accordingto the present invention (claims 8, 15), by making the diameter of thesolder fine particle smaller than the shortest distance between theperipheral edges of the adjacent pad electrodes, it enables to avoid thecontact between the solder fine particles which reached respectively onthe two adjacent electrode pads. Thereby, it is possible to more surelyprevent the solder bridges from being formed.

In the apparatus for forming the solder bumps according to claim 11, bynot connecting the bottom section of the first liquid tank for formingthe solder bumps on the substrate and the bottom section of the secondliquid tank for forming the solder fine particles, the solder fineparticles which did not form the solder bumps are not reutilized.Thereby, it is possible to improve the quality of the solder fineparticles and also to make the size of the solder fine particlesuniform.

In the apparatus for forming the solder bumps according to claim 12, byconnecting the bottom section of the first liquid tank for forming thesolder bumps on the substrate and the bottom section of the secondliquid tank for forming the solder fine particles, the solder fineparticles which did not form the solder bumps can be reutilized.Thereby, the solder can be effectively utilized without a waste.

1. A solder supplying method for forming solder coating on a metal filmthrough positioning a substrate having the metal film on a surface withthe surface facing up in a liquid which is heated to be hotter than amelting point of solder and dropping solder fine particles made of thesolder being melted on the substrate in the liquid.
 2. The soldersupplying method according to claim 1, wherein the solder fineparticles, which are dropped and come in contact with the metal film orthe solder coating, are kept in that state for a certain time untilsolder wet is caused.
 3. The solder supplying method according to claim1, wherein the solder fine particles to be dropped on the substrate arelimited to the ones whose falling speed is within a specific range.
 4. Asolder bump forming method for forming a solder bump on a pad electrodethrough: positioning a substrate having the pad electrode on a surfacewith the surface facing up in a liquid which is heated to be hotter thana melting point of solder; supplying solder fine particles made of thesolder being melted into the liquid; and dropping the solder fineparticles on the substrate.
 5. The solder bump forming method accordingto claim 4, wherein the solder fine particles are formed by breaking inthe liquid the solder being melted.
 6. The solder bump forming methodaccording to claim 4, wherein flux is contained in the liquid.
 7. Thesolder bump forming method according to claim 4, wherein an organic acidis contained in the liquid or the liquid is made of the organic acid,and the organic acid has a reduction effect which removes an oxide on ametal surface.
 8. The solder bump forming method according to claim 4,wherein a diameter of the solder fine particle is smaller than ashortest distance between peripheral edges of the pad electrodesadjacent to each other.
 9. A solder bump forming apparatus comprising: aliquid tank for enclosing a liquid heated to be hotter than a meltingpoint of solder and a substrate which has pad electrodes on a surfaceand is positioned in the liquid with the surface facing up; and a solderfine particle supplying means for supplying solder fine particles madeof the solder being melted into the liquid and dropping the solder fineparticles on the substrate.
 10. The solder bump forming apparatusaccording to claim 9, wherein the solder fine particle supplying meansforms the solder fine particles through breaking in the liquid thesolder being melted.
 11. The solder bump forming apparatus according toclaim 10, wherein: the liquid tank comprises a first liquid tank forenclosing the substrate and the liquid and a second liquid tank forenclosing the liquid and the solder being melted and sunk in the liquid;upper sections of the first liquid tank and the second liquid tankcommunicate with each other while bottom sections do not; and the solderfine particle supplying means forms the solder fine particles throughbreaking the solder being melted in the second liquid tank and suppliesthe solder fine particles to the first liquid tank from the uppersection of the second liquid tank.
 12. The solder bump forming apparatusaccording to claim 10, wherein: the liquid tank comprises a first liquidtank for enclosing the substrate, the liquid and the solder being meltedand sunk in the liquid, and a second liquid tank for enclosing theliquid and the solder being melted and sunk in the liquid; uppersections and bottom sections of the first liquid tank and the secondliquid tank communicate with each other; and the solder fine particlesupplying means forms the solder fine particles through breaking thesolder being melted in the first liquid tank and the second liquid tank,supplies the solder fine particles to the first liquid tank from theupper section of the second liquid tank, and reutilizes the solder fineparticles sunk in a bottom of the first liquid tank as the solder beingmelted.
 13. The solder bump forming apparatus according to claim 9,wherein flux is contained in the liquid.
 14. The solder bump formingapparatus according to claim 9, wherein an organic acid or flux iscontained in the liquid or the liquid is made of the organic acid, andthe organic acid or the flux has a reduction effect which removes anoxide on a metal surface.
 15. The solder bump forming apparatusaccording to claim 9, wherein a diameter of the solder fine particle issmaller than a shortest distance between peripheral edges of the padelectrodes adjacent to each other.